package crazyjava;

public class Recursive {
    public static int fn(int n){
        if(n==20){
            return 1;
        }else if(n==21){
            return 4;
        }else{
            return fn(n+2)-2*fn(n+1);
        }
    }
    public static void main(String[] args){
        System.out.println(fn(10));
    }
}
